The present invention relates generally to the field of treating wood products using fire-retardant, insecticidal, and fungicidal compositions and methods.
There are a number of properties in natural wood that make it the product of choice for building construction. Its strength, appearance, durability, accessibility and non-corrosive nature make it ideally suited for building supports, framework, decks and trims. However, wood is highly flammable and susceptible to living organisms. It is known that various compounds can be used to treat cellulosic products in order to impart a wood preservative, and flame resistant qualities thereto. The use of wood treated with such compounds came into common usage during World War II, when it was used for the construction of blimp hangars.
Due to the combustible nature of wood, building codes in virtually all U.S. municipalities restrict the use of untreated wood to certain applications. However, the preservative and/or fire-retardant treatment of wood has broadened the useful scope of both wood and wood substrates, because many of these municipalities will allow the use of treated wood as a non-combustible material in applications where untreated wood would not be permitted. Most municipalities in the United States rely on the specifications delineated within the Uniform Building Code (xe2x80x9cUBCxe2x80x9d) and Uniform Building Code Standards to certify treated wood as suitable for all types of construction. These municipalities also rely on outside certification agencies, such as Underwater Laboratories, Inc. (xe2x80x9cULxe2x80x9d) to certify which preservative and/or fire-retardant treated materials meet the criteria for strength, durability, fire-retardance and other properties.
There exists in the art a uniform basis for recognition of quality control of fire-retardant treated lumber, as required by xc2xa7207 of the UBC. In order to be used in structural applications, fire-retardant treated lumber must comply with UBC Chapter 8 Section 802 delineating the standards promulgated by the American Standard Testing Method (ASTM) E-84, which are equivalent to the standards of Underwriters Laboratories, Inc. (UL) Standard 723. The standards promulgated therein include UBC Standard 8-1 for Test Method for Surface-Burning Characteristics of Building Materials, UBC Standard 23-4 for hygroscopic properties, UBC Standard 23-5 for Design Values, UBC Chapter 8 Section 802 for flame spread, and the United States Military Specification No. MIL-L-19140E, Paragraph 4.6.5.2 (Amendment 1, dated Oct. 1, 1985) for corrosiveness. It is accepted that the certification standards promulgated by the International Conference of Building Officials (ICBO) provide the necessary procedures for testing treated wood products to determine whether the UBC standards are met. Fire-retardant treated lumber is qualified on the basis of testing in accordance with the applicable UBC standards, as conducted by an ICBO ES accredited laboratory. The quality control requirements include moisture content, solution concentration, chemical retention by gauge, fire tube tests, assay of borings, or other validated methods, as delineated in the Approved Quality Control Manual. These procedures are set forth in the ICBO Evaluation Service, Inc., Acceptance Criteria for Quality Control of Fire-Retardant Treated Lumber AC 66, Issued April 1997.
It is known that ammonium phosphates, aluminum sulfates, aluminum hydrates, or chlorinated paraffins can impart fire retardant qualities to treated wood. Most fire-retardant compounds make use of the same technical underpinning. These compounds comprise salt compositions which become acidic under elevated temperatures. These salts can form, for example, phosphoric and sulfuric acid and other, phosphate and sulfate derivatives under high temperatures. The acids and derivatives formed promote charring of the treated material during exposure to fire. The resulting char reduces flammability by insulating the material from the fire, thereby reducing flame spread and penetration. Many fire retardant compositions also include starches, such as molasses, in order to provide adequate charring. However, the use of such starches renders the treated materials susceptible to degradation by adventitious organisms such as insects and molds.
Plywood sheaths are often treated with fire-retardant compositions and used for roof decking. The temperature of roof decking at the interface between the overlying shingles and the roof deck can often exceed 170xc2x0 F. Many prior art fire-retardant compositions begin to degrade at such temperatures, resulting in acid hydrolysis at temperatures well below those present during a fire. As a result, it has been found that many roof decks constructed from plywood sheaths treated with prior art fire-retardant compositions begin to loose structural integrity. This structural degradation occurs more rapidly in warmer climates. Furthermore, the presence of moisture has been found to accelerate the rate of thermal degradation of many treated products. Thus, in many cases, the treated plywood used as roof decking may require replacement in as little as two to seven years, because the degradation of wood products used for structural purposes results in the products being unsuitable for use.
Most known fire-retardant compositions require a drying step with high heat after application to wood materials. This high-heat step often leads to premature activation of the chemical processes designed to resist flame spread during fire, leading to acid hydrolysis of the cellulose fibers in the material treated, greatly weakening the treated product by compromising the structural integrity.
Many prior art fire-retardant compositions make use of active ingredients, such as ammonium sulfates and ammoniacal copper didecyldimethylammonium which have been found to be corrosive to metal, including common metal fasteners, such as staples or nails, which are used to secure the treated materials. Thus, for treatment of materials to be secured in place with metal fasteners, such as the majority of all materials, compositions making use of less corrosive active ingredients is critical. However, many of the replacement materials, such as ammonium phosphate are highly hygroscopic which results in high moisture pick-up by the treated product. Thus, there is a need for offsetting the hygroscopicity of the non-corrosive replacement salts.
The treatment of wood with most prior art wood fire-retardant compositions has generally required the use of incising the wood with small perforations in order to assure adequate penetration of the wood with the composition. However, in incising, the fibers of the wood are cut which leads to a reduction in the structural integrity of the treated wood.
Many prior art fire-retardant compositions discolor, as well as degrade, the material treated after prolonged exposure to the elements. For example, dark, reddish-brown charred spots soon begin to appear in wood products treated with prior art compositions. This discoloration prevents the use of the treated material where an exposed natural wood finish is aesthetically desirable.
Ammoniacal copper zinc arsenate (ACZA) and chromated copper arsenate (CCA) have been used for many years as wood preservatives. However, the prior art has demonstrated the problems presented when wood preservatives and fire retardants are combined. See White et al. xe2x80x9cFlame Retardancy of Wood: Present Status Problems, and Future Fields.xe2x80x9d in Lewan ed. Recent Advances in Flame Retardancy of Polymeric Materials: Proceedings of 3d Annual BCC Conference on Flame Retardance (Business Communications Co., Stamford, Conn. (1992)). These problems include leaching of the preservative and/or fire retardant, from the wood and the staining or discoloring of wood when leach-preventing materials are added. Id.
Inorganic boron containing compounds impart fungicidal, insecticidal, and fire retardant properties to wood products. Since inorganic boron compounds are readily soluble in water, exposure to atmospheric moisture can cause leaching of the boron compounds. U.S. Pat. No. 5,612,094 (xe2x80x9cShubertxe2x80x9d) disclosed that aqueous compositions of boron compounds in and with zinc zirconium salts in which the ZrO2:B2O3 weight ratio ranged from 0.75:1 to about 10:1, provided wood preservative qualities to treated wood, including protection against fire, fungi, and termites. Shubert disclosed that the zirconium borate compositions were resistant to leaching.
Organic compounds are sometimes added to fire-retardant compositions to seal Out moisture and contain the active salt ingredient within the structure of the treated material, thereby also raising the threshold temperature at which activation occurs. For example. U.S. Pat. No. 4,461.720 (xe2x80x9cLoyvetxe2x80x9d) and U.K. Patent Application GB 2,200,363 both disclosed fire retardant compositions containing partially reacted solutions of dicyandiamide, melamine, formaldehyde, and an oxyacid of phosphorus. The Loyvet composition is a guanyl urea based solution in which the guanyl urea to melamine ratio is within the range of 5:1 to 10:1, and the formaldehyde to guanyl urea melamine mixture is within the range 1:1 to 2:1. These references disclosed that these fire retardant solutions provided improved leach resistance over simple urea solutions.
U.S. Pat. No. 5,389,309 (xe2x80x9cLopezxe2x80x9d) disclosed a urea-nitro based fire retardant solution, which included a conventional fire-retardant, such as ammonium phosphate, aluminum sulfate. aluminum hydrate. chlorinated paraffins, borax or boric acid; dicyandiamide; urea nitro; a urea/formaldehyde resin polymer in water; and a melamine and acid salt catalyst activator used to catalyze the formation of a urea/formaldehyde resin. Lopez disclosed a fire retardant solution which was non corrosive and did not require elevated temperatures to dry.
In addition to the above-described problems in the art with conventional fire-retardant compounds and with the use of untreated lumber in construction, additional problems of pest infestation and control has emerged in recent years. A dramatic example of the problem is seen in the influx of Formosan termites which are found in at least California, Hawaii, Florida, and Louisiana. The pests cause major structural damage to wood structures which can significantly compromise the stability of the wood structures. The problem is exacerbated in situations such as fires and earthquakes. Surprisingly, Formosan termites and other varieties of termites were discovered to be a significant factor in the damage caused during the Northridge, Calif. earthquake in 1994. Termites are but one adventitious organism which is deleterious to the strength of wood.
The present invention provides a method for treating flammable wood, wood products or cellulosic materials. such as those used in the construction industry, with a novel preservative composition for imparting fire retardant, insecticidal, and fungicidal properties to the treated wood products. The present invention uses an aqueous preservative composition that increases the structural strength of the treated wood products, is not corrosive to ordinary metal fasteners such as nails, screws, etc., will not leach from the treated wood products, provides moisture resistant properties to the treated wood products, does not require elevated temperatures to dry, does not attract adventitious organisms, and will not activate, hydrolyze, release nitrogen gas, or acidify at temperatures lower than those expected during a fire. The preservative composition of the present invention is also easy to handle because it is a stable aqueous solution, allowing it to be stored and shipped as a solution.
Thus, in a first aspect, the invention features a method for treating wood products to impart fire, insect, and fungus resistance qualities. The method includes the steps of applying the stable aqueous preservative composition to a wood product. The wood product can be any cellulosic-containing material, such as wood, lumber, wood substrates, paper, plywood, wood particle board, loose fill or panels, oriented strand board, mineral fiber board, modified density overlay, or cellulosic insulation, including loose fill or panel type applications, etc. The preservative composition penetrates the wood product without first incising, thereby maintaining the structural integrity of the treated wood product. The method then involves drying the treated wood product until the hydroscopic moisture content is at or below about 19%. The drying step can be completed using ambient air, without using high heat.
In a distinct embodiment. the method includes treating a wood product under pressure by applying the aqueous preservative composition for a sufficient time to diffuse the preservative composition evenly throughout the treated wood product while maintaining, a pressure which exceeds atmospheric pressure, but is less than about 200 psig for the duration of the treatment process. In a preferred embodiment, the pressure is maintained between 75 and 125 psig. In another distinct embodiment the wood product is first exposed to a vacuum, prior to application of the preservative composition, in order to reduce the moisture content, and then treated under pressure. The vacuum can range from 5xe2x80x3 Hg. to 25xe2x80x3 Hg. After a vacuum is applied, the treating pressure and/or treatment time can then be reduced accordingly.
The invention features a stable, non-corrosive preservative composition for imparting fire, insect, and fungus resistance qualities to wood products comprising an aqueous solution of a boron-source composition selected from the group consisting of boric acid and the water-soluble salts thereof, a melamine binder resin, and an urea casein activator resin. The amount of the boron source composition melamine binder resin, and urea casein activator resin are adjusted so that the resultant preservative composition has a weight ration of boron source to melamine ranging from 1.30:1 to 9.6:1, preferably about 8:1, and a weight ration of urea casein activator resin to melamine binder resin ranging from 1:20 to 1:4, preferably about 5.5:1.
The boron-source composition can be boric acid or the water-soluble salts of boric acid, including sodium tetraborate decahydrate, sodium tetraborate pentahydrate, sodium octaborate tetrahydrate, sodium metaborates, sodium perborate hydrates, potassium tetraborate, sodium pentaborate, ammonium pentaborate hydrate, and hydrasodium tetraborate, potassium metaborate, any alkali metal borate salt, or combinations of these compounds. Preferably, the boron source composition is disodium octaborate tetrahydrate, which is commercially available from IMC Chemical, Overland Park, K.S. or U.S. Borax, Inc., Valencia, Calif. The boron-source compound is a primary fire retardant, as well as an insecticidal and fungicidal agent.
The melamine binder resin can be any amino resin made from melamine (2,4,6-triamino symtriazine) and formaldehyde, typically used for marine graded plywood, or as a nitrogen source in binders used to make pipe insulation. The melamine binder resin is characterized by a viscosity (@ 78xc2x0 F.) ranging from 600-1000, a pH ranging from 8.6-9.7, a flee formaldehyde concentration less than 0.5% by weight, a specific gravity of about 1.2, and a degree of polymerization of about 2.1. The melamine-binder resin acts as a nitrogen-liberating compound, releasing nitrogen in the presence of a flame. The melamine binder resin includes modified melamine-formaldehyde resins such as GP(copyright) 482T23 Thermal Insulation Binder Resin or GP(copyright) 476T19 Melamine Insulation Resin, both commercially available from Georgia-Pacific Resins, Inc. Decatur, Ga., or MB 46-50 Liquid Melamine Adhesive commercially available from National Casein or Cytek, located in Santa Ana, Calif., and Jersey City, N.J., respectively. Preferably, the melamine binder resin is a liquid.
The urea casein activator resin can be any liquid urea formaldehyde resin typically used for marine or N graded plywood. The casein resin activator is characterized by a viscosity ( 78xc2x0 F.) of about 550cp, solids percentage of 63%-67%, a pH of about 7.5, a specific gravity ranging from 1.20-1.38, and a formaldehyde concentration less than 1.5%. The urea casein activator resin is also nitrogen-liberating compound, which releases nitrogen in the presence of a flame. Preferably, the urea casein activator resin is #750 Urea Resin Adhesive or GP(copyright) 1967, commercially available from National Casein, Santa Ana, Calif. and Georgia Pacific Resins, Decatur, Ga., respectively.
After application to the treated wood products, the urea casein activator resin initiates a polymerization reaction involving the melamine binder resin. The resulting melamine polymer creates a substantially impervious barrier to atmospheric moisture and also binds or encapsulates the wood preservative composition to the treated wood product to prevent leaching of the boron source composition from the treated wood product through solubalization by atmospheric moisture. The melamine polymer acts as a nitrogen-liberating compound, Which releases nitrogen in the presence of a flame.
In still another aspect of the present invention, the wood preservative composition is formulated in combination with a conventional glue substrate or pigment. In a preferred embodiment, this fire-retardant glue is used to bind the laminate structure of plywood and similar laminar wood structures.
In a related aspect, the invention features a treated wood product containing an insecticidal, fungicidal, and fire retardant amount of a melamine polymer borate preservative that is substantially impervious to moisture, so as to limit leaching of the preservative composition from the treated wood product and to further limit the penetration of water into the treated wood product. As a further aspect of the present invention, the treated wood product. is also made structurally stronger when compared to an untreated wood product after treatment with the wood preservative composition of the present invention and sufficient aging to allow for sufficient polymerization. Preferably, the treated wood product is lumber, plywood. wood particle board, oriented strand board, mineral fiber board, or modified density overlay. In a preferred embodiment, the treated wood product contains at least 0.1 7 lb/ft3 of B2O3 if the treated wood is to be used in above ground applications, or 0.28 lb/ft3 of B2O3, if the treated wood is to be used in ground contact applications. The treated wood products are resistant to Fomosan termites.
In a further related aspect, the invention features a process of preparing a preservative composition used for treating wood products, comprising mixing a primary fire-retardant agent containing a source of boron, selected from the group of boric acid and the water-soluble salts thereof, a polymer binder resin, and a polymer activator resin; and mixing until a smooth composition is obtained. Preferably continuous mixing of the preservative composition is provided throughout the process.
The present invention provides superior fire retardant pest control and/or fungus control compositions and treatments, including the use of superior resins and material processing procedures, heretofore never applied. Further objects, features and other advantages of the present invention will become apparent from the ensuing detailed description and from the claims.
The preservative compositions of this invention are prepared by mixing one or more of the boron source compositions, the melamine binder resin, and the urea casein activator resin in an aqueous solution. Thus, the boron source compositions can first be dissolved in water and then can be mixed with the melamine binder resin and the urea casein activator resin, in that order. The melamine binder resin and urea casein activator resin can be each individually mixed in water before addition to the other ingredients of the preservative composition. This allows the proper buffering effect to occur. Generally, the urea casein activator resin is added last. The preservative composition can also be formed by first combining the melamine binder resin and the urea casein activator resin with water to form an aqueous solution. The aqueous solution of the melamine binder urea casein resin activator can then be added to an aqueous solution of the boron-source composition. Alternatively, the preservative composition can be formed in a step process within the wood products themselves by first applying the boron-source composition and then applying an aqueous solution comprising the melamine binder resin and the urea casein activator resin.
The boron-source composition is a primary fire retardant, as well as an insecticidal and fungicidal agent. The boron-source composition can be boric acid or the water-soluble salts of boric acid. Generally, however, the preservatives may be any hydrate of an alkali metal salt or boric acid. Such salts may include sodium, potassium, lithium, and the like. Compositions having mono-, di-, tri, or other plural salt moieties are contemplated. Similarly, varying degrees of hydration are also contemplated.
Specific compositions include sodium tetraborate decahydrate, sodium tetraborate pentahydrate, sodium octaborate tetrahydrate, sodium metaborates, sodium perborate hydrates, potassium tetraborate, sodium pentaborate, ammonium pentaborate hydrate, and hydrasodium tetraborate, potassium metaborate, any alkali metal borate salt, or combinations of these compounds. Various mixtures of the boron source compositions can also serve as the primary fire retardant. Most preferably, the boron source compound is disodium octaborate tetrahydrate Na2B8O13,4H2O, which is commercially available from sources such as IMC Chemical, Overland Park, K.S. or U.S. Borax, Inc., Valencia, Calif. It is toxic to fungus and wood-destroying insects, including termites. Disodium octaborate tetrahydrate forms finer crystals which more readily penetrate the pores of the porous cellulosic materials to which the compositions are applied. This material also has a high heat activation. In other words, high temperatures are required to convert the disodium octaborate tetrahydrate into the acidic forms resulting in the fire-retardant effect.
Typically, disodium octaborate tetrahydrate contains about 14.2-15% Na2O, 67.3-67.5% B2O3 and 17.5-17.6% water of crystallization. The boron-source composition is included in the composition in a range of from about 5% to about 25% by weight of the total aqueous solution. or more preferably from about 10% to about 20%.
The melamine binder resin is a modified melamine binder resin, such as those melamine resins which are primarily used for marine graded and N graded plywood, or as a nitrogen source in binders to make pipe insulation. The melamine binder resin can be any amino resin made from melamine (2,4,6-triamino symtriazine) and formaldehyde, characterized by a viscosity (@ 78xc2x0 F.) ranging from 600-1000, a pH ranging from 8.6-9.7 a free formaldehyde concentration less than 0.5%, by weight, a specific gravity of about 1.2 to 1.24, and a degree of polymerization of about 2.1. The melamine-binder resin includes modified melamine-formaldehyde resins such as GP(copyright) 482T23 Thermal Insulation Binder Resin or GPO(copyright) 476T19 Melamine Insulation Resin, commercially available from Georgia-Pacific Resins, Inc, Dekatur, Ga., or MB 46-50 Liquid Melamine Adhesive, commercially available from National Casein or Cytek, Santa Ana, Calif. and Jersey City, N.J. respectively. Preferably, the polymer binder resin is a liquid. The melamine binder resin is a nitrogen-liberating compound, which releases nitrogen in the presence of a flame.
The melamine binder resin is included in the composition in a range from about 1% to about 13% by weight of the total aqueous solution. The ratio of the boron-source composition to the melamine binder resin ranges from about 1.3:1 to 9.6:1, preferably about 8:1. Similarly the BO to melamine weight ration ranges from about 0.9:1 to 6.5:1 preferably about 5.4:1.
The use of a melamine binder resin provides a composition of superior characteristics. The melamine binder resin provides a casing for the fire retardant. Thus, the treated materials are protected from water damage and from other elements, thereby preventing the primary fire retardant from leaching from the treated wood product. The protection of the material from water offsets the hygroscopic properties of many primary fire-retardants, such as ammonium phosphates. In addition, the use of melamine binder resins actually enhances the strength of the treated wood relative to other treated wood products or untreated wood products. Unlike many prior art fire retardant compositions, the composition of the present invention does not significantly corrode metals. Additionally, the preservative composition is absorbed easily by wood and provides structural rigidity thereto.
Although melamine resins are widely used in the wood products industry as molding compounds, fillers, adhesives and for laminating, a major drawback is its limited stability. Accordingly, storage of melamine is difficult, and liquid solutions containing melamine typically have a very short working period before they will set. Thus, melamine solutions must be replaced frequently, resulting in both increased handling and material costs.
In accordance with the invention, it has been unexpectedly discovered that the preservative composition can be improved and stability enhanced through the utilization of liquid suspensions of melamine-binder resin. The liquid suspensions of melamine-binder resin are prepared by dissolving a melamine-binder resin in water, and then buffering with phosphates at a slightly acidic pH of approximately 6.0 to about 6.5. The total nitrogen content of the buffered malamine-binder resin solution is in the range of about 17.2% to about 18.3% by weight (including water) and the total phosphate concentration is in the range of about 15.7% to about 16.8% by weight (including water). The resulting aqueous solution has a specific gravity of about 1.28 g/ml and a refractive index of 1.457. Through use of the suspensions, it is possible to blend fire-retardant compositions with improved consistency, improved specific gravity and improved stability. As such, wood treated with preservatives containing liquid suspensions of melamine-binder resin exhibits improved fire-retardant qualities.
In order to polymerize the melamine binder resin, an activator is generally required. A urea casein activator resin provides excellent results in this regard. The urea casein activator resin can be any liquid urea resin adhesive with a viscosity of about 550 cp (@ 78xc2x0 F.), solids percentage of 63% -67%, a pH of about 7.5, a specific gravity ranging from 1.20-1.38, and a formaldehyde concentration less than 1.5%. The urea casein activator resin includes #750 Urea Resin Adhesive or GP(copyright) 1967 Casein, commercially available from National Casein, Santa Ana, Calif. and Georgia Pacific Resins, Decatur, Ga., respectively. The urea casein activator resin is a nitrogen-liberating compound, which releases nitrogen in the presence of a flame. Preferably, the urea casein activator resin is a liquid.
The urea casein activator resin ranges in an amount of from about 0.16 to 3.5% by weight (including water) of the aqueous wood preservative composition. Higher amounts of the urea casein activator resin will cause the melamine binder resin to polymerize very quickly and at lower temperatures, while lower amounts will require longer curing times and higher temperatures. Thus preferably, the urea casein activator resin is added within the weight ratio range of 1:4 to 1:20 in relation to the melamine binder resin in order to allow for adequate shelf life of the aqueous preservative composition while still allowing for practicable polymerization times and conditions.
The urea casein activator resin is suspended separately in water, prior to being mixed with the other components of the composition in order to assure complete mixing. Typically, a 1:1 volumetric aqueous solution is prepared.
In addition, a concentrate solution comprising an aqueous solution of the melamine binder resin and the urea casein activator resin can be prepared. This concentrate solution is characterized by a specific gravity ranging from 1.14 through 1.20, a percent solids ranging from 30% to 82%, a pH ranging from 7.0 through 9.5, and a refractive index ranging from 1.39 through 1.47. As stated above, the concentrate solution has a melamine binder resin to urea casein activator resin weight ratio ranging from 1:4 to 1:20.
The melamine binder resin and the urea casein activator resin are nitrogen containing compounds which liberate gaseous nitrogen during burning (sometimes referred to herein as xe2x80x9cnitrogen liberating compoundsxe2x80x9d), resulting in foaming of the carbonized layer on the other surface of the treated material. This foaming increases the thickness of the carbonized layer, resulting in increased insulation of the unburned material below. At the same time the liberated nitrogen serves to dilute oxygen in the vicinity of the material to retard combustion.
In formulating the preservative composition of the present invention, the specific gravity ranges from 1.030-1.075. The preservative composition of the present invention is characterized by a Hydrometer table (attached as Appendix A) relating the specific gravity, ambient temperature, and percent solids of the preservative composition. At 25xc2x0 C., the preservative composition, pursuant to the Hydrometer Table, the percent solids ranges from 3.3% (40xc2x0 F., S.G.=1.03) to 20.67% (119xc2x0 F., S.G.=1.075).
In a highly preferred embodiment, the fire-preservative composition is prepared according to the following weight percentages (excluding water):
This ratio achieves the appropriate pH in the resulting composition.
The wood preservative and fire-retardant compositions prepared utilizing liquid solutions of melamine binder resin and urea casein activator resin, and containing the above formulation, possess very smooth, clear consistencies and are rapidly and deeply absorbed into wood, indicating deeper and more effective wood preservative penetration. Conventional additives can also be added to the preservative composition, such as coloring agents, odor modifying agents, thickeners, or glue, depending upon the wood treatment application.
As will be appreciated by those in the art, other melamine binder resin and urea casein activator resin systems could be used in accordance with the invention. The basic consideration applicable to resin activator systems is that they (i) do not materially detract from the strength of the treated wood and preferably enhance the structural integrity of the treated wood, (ii) provide a sealing function to limit leaching and limit water absorption, and (iii) add to the fire-retardant qualities of treated wood, (iv) and can be combined to provide a stable solution which can be stored and reused without any depreciable effect on the wood preservative qualities of the preservative composition.
As will be appreciated by those of ordinary skill in the art, other wood preservatives, fire retardants, insecticidal agents, or fungicidal agents can also be admixed with the preservative composition in accordance with the invention to obtain a similar preservative effect.
The wood preservative compositions can be applied to any flammable material to decrease flammability. For example, the compositions can be applied to porous materials, including cellulosic products such as paper, wood, lumber, plywood, wood particle board oriented strand board, mineral fiber board, modified density overlay, wood substrates, cellulose insulation including loose fiber or panel-type. The compositions can be applied in any conventional manner which are well known in the wood preserving and fire retardant arts, including soaking, spraying, brushing, rolling, pressure treating, surface application, by adding the composition during manufacture and the like. The preservative compositions can be applied to existing wood or structural members during retrofit or renovation projects in which the wood must be treated in place. In practicing the method of this invention, the wood product is treated with the preservative composition in a manner so as to impregnate the wood product and deposit and distribute a fire retardant, insecticidal, and fungicidal amount of the wood preservative to the wood product being treated.
Because the composition is stable as a liquid, any remaining or excess composition from a treatment process can be recovered and reused, resulting in substantial material cost savings. Advantageously, wood treated with the composition of the present invention requires no incising to permit adequate penetration, resulting in a substantial reduction in handling costs for wood treated with the present preservative composition.
Materials that are not readily penetrated, such as wood, are preferably treated by exposure to the preservative composition at an elevated pressure in a pressure vessel or other equivalent equipment, such as is known to one of skill in the art. The pressure must exceed atmospheric pressure but is less than about 200 psig for the duration of the treatment process. Preferably. the pressure is maintained between 75 and 125 psig. In addition, the wood product can first be exposed to a vacuum ranging from 5 inches to 25 inches (Hg) in order to reduce the moisture content prior to pressure treating with the wood preservative composition.
Preferably, the separate pieces of material to be treated are separated prior to treatment to allow even access to the composition. This separation can be accomplished by a process known as xe2x80x9csticking,xe2x80x9d which comprises placing small sticks between the pieces of material, to provide separation.
In order to recover excess preservative composition after the wood products have been treated, the materials can optionally be brought to a recovery area where excess composition is allowed to drip off the materials and is collected for reuse.
The materials can be dried by exposure to climatic air flow. Drying will occur more rapidly under warmer, drier conditions. The drying area can be outdoors in a warm, dry climate, or indoors when required by outside weather conditions. Preferably, in order to promote drying, the treated materials are separated to allow the to air flow around. As an advantage, if the materials are xe2x80x9cstickedxe2x80x9d prior to the treatment process, they can be left in this sticked configuration in order to maintain separation during the drying process.
For wood, the drying proceeds until the hygroscopic moisture content is at a maximum of 19% or below. Wood treated by pressure treatment will be impregnated with the preservative composition to provide superior fire-retardance and structural rigidity. After treatment with the preservative composition, the resultant wood products exhibit fire retardant, insecticidal, and fungicidal properties. In operation, following the drying of the treated wood product. The resulting polymer formed by the curing of the melamine binder resin binds or encapsulates the preservative within the structure of the wood products, which deters or prevents leaching of the preservative. The resultant treated wood products containing the melamine polymer borate preservative are thus extremely useful in any type of rigorous service where exposure to atmospheric moisture is either frequent or extreme, such as outdoor decking, patio roofs, exterior siding, etc. Moreover, planing of such treated wood up to about as much as {fraction (1/16)} inch will not remove all the preservative composition, and thus will not remove the fire-retardant characteristics of the treated wood. Additionally, the deeper planing of one side of a four-sided treated board will leave substantial fire-retardant qualities in the board.
In addition, the preservative composition of the present invention can be applied in a single charge. As a result, in a single treating process a wood product can be prepared that has superior fire retarding properties as well as providing superior pest and fungus resistance without reducing fire-retardant effect. Further, wood products treated with the preservative composition are not materially affected in their strength relative to wood not containing the preservative compositions.
The composition of the present invention provides a number of properties that differ greatly and substantially in kind and scope from prior art fire-retardant and preservative compositions, providing several significant advantages. For example, the composition is substantially non-corrosive to metal and has no starches to degrade wood fiber or attract adventitious organisms. The preservative composition does not require high heat for drying, such as that produced through the use of a kiln, thereby eliminating any premature activation of the fire-retardant during the drying step. Moreover, the composition has a high heat of activation, thereby substantially eliminating the degradation of treated materials by exposure to temperatures below those found in a fire, such as those found in roof decks or rafters. Additionally, the substantial elimination of premature activation inhibits the formation of discoloration which prevents the use of the treated materials where an exposed natural finish is aesthetically desirable.
As stated above, the composition also provides structural rigidity to the material to which it is applied. Thus, should the treated material begin to decay from any of a variety of causes, structural rigidity is retained. Also, the composition is stable for long periods of times, which allows the composition to be prepared and stored for shipment and also allows for reuse of recovered preservative composition after the treatment process.
Preferably, the treated wood products contain 0.17 pounds per cubic foot B2O3, if the treated wood is to be used in above-ground applications, and 0.28 pounds per cubic foot B2O3 if the treated wood is to be used in ground contact applications.
Wood products treated with the preservative composition of the present invention meet or exceed ICBO ES standard AC66, Acceptance Criteria for Quality Control Fire Retardant-Treated Lumber, April 1997, including the following tests:
1. U.L. 723, ASTM E-84, NFPA 255-Test for Surface Burning Characteristics of Building Materials;
2. ASTM D-3201-Fire Retardant Wood Test for Hydroscopic Properties;
3. ASTM D-143-83-Determination of Potential Strength Reduction; Characteristics Due to Effects of Elevated Temperature and Moisture
4. ASTM D-55 16-94-Standard Test for Evaluating The Flexural Properties of Fire Retardant Treated Soft Wood Plywood Exposed to Elevated Temperatures;
5. Military Specifications MIL-L-19140E, paragraph 4.6.5.2-Corrosiveness Test, Lumber and Plywood Fire Retardant Treated;
6. Military Specifications MIL-L-19140E, paragraph 3.4-Strength Retention, Lumber and Plywood Fire Retardant Treated.
Wood products treated with the composition of the present invention also conforms to the mandated Uniform Building Code requirements and the Uniform Building Code Standards for pest control and fire retardant treated wood for structural applications in buildings or structures, including the standard for flame spread, hydroscopic properties, strength, and corrosiveness.